When the LGA 2011 platform was introduced in November last year, we took the opportunity of testing the Core i7-3960X with its price tag of no less than $999. Thankfully, the i7-3960X isn’t the only LGA 2011 processor around as Intel is now also offering the i7-3930K at $583 and an even more affordable model, the Core i7-3820, at $285.
Three CPUs for one platform
As this table shows, the Core i7-3930K has a slightly lower clock than the 3960X and a 12 MB rather than a 15 MB L3 cache. The i7-3820 stands alone with just four cores and a 10 MB L3 cache. Moreover, its multiplier is limited to x43, or 4 notches above Turbo mode, whereas the X and K models can go up to x57.
As we saw in the article on LGA 2011 however
, the platform enables overclocking by the bus and this makes clocks upwards of 5 GHz accessible if required.
All the following tests were carried out using the same configuration as the one used in the report on the Core i7-3960X
, with the AMD FX processors being tested here with the latest Windows 7 patches available
Let's start, then, by looking at overclocking for these two processors. Remember on the i7-3960X we managed 4.6 GHz with the bios voltage fixed at 1.45v on the DX79SI motherboard. Now HWiNFO64
can give the vCore reading for the additional CHL8328 chip and we therefore also give this value in the table. We validated each clock for 15 minutes in Prime95 and the energy consumption given is that measured in load in this application.
To start with, the 3930K does better than the 3960X, with a bios voltage of only 1.4v (actually corresponding to 1.27v in load) required to clock it to 4.6 GHz. We managed to stabilise it at 4.7 GHz and we even managed to reach 4.8 GHz at 1.5v (actually 1.35v) though unfortunately at this voltage, energy consumption at the ATX12V exceeds 300 Watts and the Noctua NH-12UP SE2 no longer has sufficient cooling capacity. Note moreover that there’s a decent undervolting margin and that the 3930K can be overclocked quite easily up to 4.4 GHz.
The i7-3820 behaves similarly if we confine ourselves to the bios voltage, though the actual voltage applied to the processor is higher (the drop in voltage in comparison to the voltage requested in the bios being a function of the power requested). We managed to stabilise it at 4.7 GHz but not at 4.8 GHz. Beyond 4.3 GHz, we didn’t overclock using the multiplier only, as this is locked at x43, but also the clock multiplier. Thus we managed 4.7 GHz (4697 MHz to be precise) using a x37 multiplier and a bus at 127 MHz (101.6 MHz x 1.25).